This invention relates generally to veneer restoration of teeth and more particularly to an improved porcelain veneer and method of forming and applying to teeth a glazed porcelain labial veneer or restoration.
As noted in the extensive discussions of the restoration of teeth by the applications of laminar overlays in U.S. Pat. Nos. 3,986,261 and 4,433,959 issued to Faunce and 4,473,353 issued to Greggs, many structural and cosmetic deficiencies of teeth can be corrected by the preparation and bonding permanently to the tooth being treated an outer layer thereby creating a new veneer. For many types of situations, such a procedure is a marked improvement over the formation of a crown which involves the use of expensive metal materials, such as gold, and extensive dental chair time to reduce drastically or reshape the affected tooth.
In the earlier Faunce patent noted above method and apparatus are taught to restore teeth by adhering to the teeth a properly colored polymerized, preformed plastic facing. In the later Faunce patent, the concept is improved upon by presenting the use of a composite laminate dental veneer in which it is possible to combine an inner lamination capable of efficient bonding to the labial enamel surface of the tooth with an outer lamination composed of dense, stain-resistant materials such as a cross-linked polymer and various vitreous materials such as ceramic material, glass and the like. An additive and subtractive color system is employed in the outer laminate to achieve the desired cosmetic effect.
The use of plastic and plastic-based materials to accomplish the tooth restoration while in many ways and situations an improvement over the use of crowns does suffer certain drawbacks which limit their usefulness and application. Due to the porosity of plastic materials, there are problems of long-term color stability, while wear resistance tends to be low. When laminates are employed, the thickness required for their most effective use has been found in many cases to lead to inflammation of gingival tissue. Other problems which have appeared relate to toxicity of materials themselves and difficulties involved in obtaining the desired color.
The patent to Greggs teaches the cosmetic restoration of teeth employing for the labial veneer a glazed porcelain material custom made for a patient's tooth and thereafter chemically and mechanically bonded to the tooth. The use of porcelain avoids many of the drawbacks and problems associated with plastic materials, however, in the method taught by Greggs there are certain limitations and deficiencies. The method taught by the patentee is to prepare initially a model of the patient's tooth or teeth from which is prepared a Pindex model. After trimming and undercutting the tooth die, platinum foil is placed over the labial surface of the tooth die. The platinum matrix is removed for decontamination and then replaced on the die for brushing with porcelain powder. The foil matrix is removed for firing and then replaced on the die for finishing, trimming, and contouring. The matrix is again removed from the die for cleaning and separation of the foil from the porcelain veneer. The tooth and veneer are treated at their contacting surfaces and the venner then bonded to the tooth.
In the patented method of Greggs briefly described above, some of the tooth, especially at the bottom, must be stripped away to accommodate the thickness of the platinum foil. In addition, the frequent mounting and removal of the porcelain requires the veneer to be thicker along the edges than is actually required on the tooth. Furthermore, when the metal foil is peeled away from the veneer, some of the porcelain along its edges is removed as well creating problems of providing a smooth transition from the procelain veneer to the tooth. The peeling away process just described, which is done in the laboratory, has proven to be a little tricky since the platinum has to be teased away from the porcelain, incurring a risk that the veneer will be damaged and the whole process has to be repeated.